For that purpose a position detector can comprise a sensor portion including at least one permanent magnet which serves as an exciter magnet and which moves with the body whose movements are to be counted, that is to say for example with a rotating shaft or a reciprocating machine carriage, in which respect it is generally fixed directly to that body or is coupled thereto in such a way that it reflects the movement thereof.
In addition the sensor portion of the position detector has a ‘ferromagnetic element’ which is referred to in that fashion herein and which comprises a combination of hard-magnetic and/or soft-magnetic components which, upon the application of an external magnetic field of given magnitude, by virtue of an abrupt change in its consistency (for example switching and/or alignment of a large number of the Weiss domains present therein) and/or geometry (change in position of ferromagnetic components in space), result in an abrupt change in the magnetic flux and thus in a corresponding voltage pulse of given power in a coil surrounding same. The abrupt change in the ferromagnetic element is therefore described by an abrupt switching of the Weiss domains or by an abrupt change in reluctance.
A particular configuration of the first-mentioned group are pulse and Wiegand wires which do not make use of any macroscopic mechanical effect in production of the above-mentioned voltage pulses.
A representative of the second group in which mechanical macroscopic effects—here storage of the subsequently produced electrical energy in a spring—are used are magnetic reed contacts, as are set forth in U.S. Pat. No. 6,628,741. Major disadvantages precisely of that specific structure are mechanical fatigue and uncontrolled bouncing of the contacts as well as the slight measuring effect. A minimal solution which is optimum in terms of cost is scarcely to be achieved in that respect.
EP 0 658 745 A2 discloses a position sensor in which the ferromagnetic element comprises a rotatably mounted permanent magnet and an iron core, to which the rotatably mounted permanent magnet ‘holds on’ until the magnetic repulsion force which the approaching exciter magnet exerts thereon becomes so great that it overcomes the holding force between the iron core and the rotatably mounted permanent magnet and the latter abruptly rotates about its axis. That causes an abrupt change in the position of the Weiss domains and therewith the magnetic flux which passes through an induction coil wound on the iron core (large dΦ/dt), and a usable voltage pulse is induced in that coil.
What is common to all those solutions is that the respectively induced voltage pulse not only serves as a signal pulse to be counted, but it can also be used for the power supply for at least a part of the electronic system arranged downstream of the sensor portion, so that the system is capable, without an external supply of electrical energy, of executing the counting and storage operations required for detecting the movement to be monitored, that is to say for example for counting the revolutions of a shaft or the reciprocating movements of a carriage and storing the count value obtained in that situation so that such value is available for an external user.